1. Field of the Invention
This invention relates to a humidified gases delivery apparatus and methods for controlling same.
2. Description of the Related Art
A number of methods and systems are known in the art for assisting a patient's breathing. Continuous Positive Airway Pressure (CPAP) involves administration of air under pressure to a patient, usually by a patient interface like a mask. CPAP is usually used to treat snoring and Obstructive Sleep Apnea (OSA). More complete breathing support is provided by a ventilator.
There are problems associated with air delivery to the airways of patient's. Mucosal drying is one such problem. Mucosal drying is uncomfortable and may awaken patients during the night. Rebound nasal congestion commonly occurs during the following day, simulating a viral infection.
Such symptoms can also occur in a hospital environment when patients are on a respirator. Typically patients in this situation are intubated but alternatively air may be delivered to the patient via other patient interfaces like masks or nasal cannula. Patients in the hospital environment can also suffer from mucosal drying, rebound nasal congestion and also from dryness, irritation and inflammation of the throat due to intubation. These problems all cause distress to the patient and may lead to further respiratory problems.
A number of methods have been employed to combat the symptoms and conditions described earlier. Some of the methods involve pharmacologic agents to reduce nasal disease or heating the patient's room. The most commonly employed method is humidification of the gases delivered to the patient. The humidified gases go some way to reducing or minimising the problems caused by air or gases delivery to a patient. Humidifiers and methods of humidifying breathing gases are known in the art. Most common humidification methods employ a humidification chamber including a reservoir of water and heater plate. The water is heated to create water vapour and gases are passed through the humidification chamber. The gases collect and hold the water vapour and are hence humidified. The humidification chamber can only hold a finite amount of water and needs to be refilled by the user or by a hospital worker in a hospital environment. Accordingly the user or health professional needs to monitor the water level within the chamber and add more water when required. This can be a tedious task and can be overlooked. A level sensor connected within the chamber is one way to measure the level of water within the humidification chamber. This is too difficult to implement and can be cumbersome. The level sensor is difficult to implement because it requires electrical connections within the humidification chamber, the sensor requires calibration and the sensor can interfere with the humidification of gases.
US 2008/0142019 discloses a high flow therapy system including a non sealing respiratory interface with a sensor disposed near it. The system also includes a humidification chamber to humidify gases and a heater plate to heat the contents of the humidification chamber. The system includes a microprocessor to control the heater plate and measure the pressure of gases delivered. The document discloses monitoring temperature and power data of the heater plate to determine the status of the water level in the humidity chamber and can trigger automatic refill of the chamber.
US 2002/0112725 discloses a breathing assistance apparatus for delivering humidified gases to a patient. The system includes a humidification chamber with a heater plate and a microprocessor to control the heating of the heater plate. The document discloses a method of determining the amount of power required to heat the contents of the humidifier to the appropriate temperature such that the gases are humidified to their correct level.
US 2004/0079370 discloses a flow probe for use in a humidification system. The probe provides temperature and flow rate sensing. The document discloses a “water out alarm” that warns a user when the level of water within the humidification chamber is too low. The system calculates thermal conductivity based on the heater plate power requirement, heater plate temperature and chamber temperature. The controller compares this calculated thermal conductivity with a threshold value. If the threshold value is greater than the thermal conductivity then the level of water is too low.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.